International Journal of Recent Engineering Science (IJRES), Volume 7 Issue 2 March - April 2020
ISSN: 2349 – 7157 www.ijresonline.com 13
Energy Efficiency of the NBRRI Interlocking
Compressed Stabilized Earth Blocks For
Sustainable Buildings in Nigeria Timothy Danjuma
Nigerian Building and Road Research Institute (NBRRI), North-Central Zonal Office, Jos, Plateau State, Nigeria
Abstract
The rising rate of global warming is leading to increase
in energy demand for cooling. The amount of energy
consumed by building materials is an important factor
in determining the energy efficiency of the building.
Strength, economy and aesthetics are parameters more
sought after when selecting building materials. Thermal
properties of building materials which is an important
parameter in determining the energy efficiency are the
least sought after. For buildings to be sustainable, they
must have low energy requirements. In this study, the
importance of selection of CSEB in designing energy
efficient building is considered and discussed. The
coefficient of Thermal Conductivity of the NBRRI
interlocking CSEB is found to be 0.4765 Wm-1K-1
which is within the range of coefficient of Thermal
Conductivity of Building Bricks (0.35 – 0.7) Wm-1K-1.
This low value of Thermal Conductivity shows that
CSEB is the most energy efficient walling material
among other alternative walling materials.
Keyword: CSEB, Thermal Conductivity, Energy
Efficiency, Sustainability.
I. INTRODUCTION
History of Walling Materials
Building materials have been used for centuries, in a
variety of ways, to provide safe, climatically
comfortable, and easy-to-construct habitats and
shelters. People’s exact choices of material have often
been determined by the availability of local materials
and the demands of nature.
The earliest humans may have lived in caves and used
trees for housing, but eventually, they learned how to
innovate and use natural materials such as soil, stone,
and wood, which were readily available around them, in
the building of houses and shelters. Mud and clay were
among the first building materials they used because of
their ease of mouldability and their adhesive properties
when used with natural fibres. The adhesive quality of
clay made it easy to work with and form into shapes.
People used straw, grass, husks and other agricultural
waste and fibres to make the structures more durable
and provide the strength to cope with severe weather
conditions. They added dung to such mixtures, and
typically used wooden moulds to form adobe. Earth
was often compacted using wooden planks to construct
walls, known as “rammed” walls, and other building
structures [1].
In recent times, humans have developed more advanced
and versatile composite building materials such as
concrete, cement, and flowable and aerated concrete.
Concrete is generally made of sand or gravel, mixed
with cement and water. When the mixture dries, it
becomes hard and stone-like. Before the mixture sets, it
can easily be poured into moulds and formed into
different shapes. Because concrete is brittle, it is often
reinforced with steel or other metals. Now, even fibre
reinforced concrete is used extensively in the
construction of structures for specialist applications [1].
New technology has also made construction using
metal more practical than before. Most high-rise
buildings and skyscrapers are built using frames made
from steel or other metals. While steel was traditionally
the favoured metal for such constructions, new alloys
are now sometimes preferred on the basis of their
resistance to corrosion.
Light-weight concrete can be used to make buildings
lighter, save materials, and make structures more stable
and durable. Plastic is another widely used modern
building material. Formed from polymers, plastics can
be moulded easily while in their liquid state. Compared
with metal and many other materials, plastic are less
dense and lower in cost
Plastic is often used for pipes and in building interiors.
Nowadays, wood-plastic composite offers a forest-
produced wood and helps save natural resources.
Modern buildings often use glass, not only for windows
but as the primary exterior building material. Glass
skyscrapers and other structures have become popular
as a result of their aesthetic appeal. Transparent glass
International Journal of Recent Engineering Science (IJRES), Volume 7 Issue 2 March - April 2020
ISSN: 2349 – 7157 www.ijresonline.com 14
also allows natural light to be used to illuminate the
interiors of buildings.
In spite of all these developments, which are especially
relevant for those in higher income groups and urban
sectors, people living in semi-urban areas and village-
dwellers still use various forms of earth blocks, which
are more readily available and have superior thermal
and acoustic properties [1].
Compressed Stabilized Earth Blocks (CSEB)
The compressed stabilized Earth block is the modern
descendent of the moulded earth block, more
commonly known as the adobe block. It is estimated
that about 1.7 billion people of the world’s population
live in earthen houses: About 50 % of the population in
the developing countries, and at least 20% of the urban
and suburban populations [2]. The idea of compacting
earth to improve the quality and performance of
moulded earth blocks is, however, far from new, and it
was with wooden tamps that the first compressed earth
blocks were produced. This process is still used in some
parts of the world. Earth blocks are a construction
material made primarily from soil. Types of earth block
include compressed earth blocks, compressed stabilized
earth blocks, and stabilized earth blocks. Compressed
stabilized earth blocks are building materials made
primarily from damp soil which is compressed, at high
pressure, to form blocks. If the blocks are also
stabilized, using a chemical binding agent such as
Portland cement, they are known as compressed
stabilized earth blocks. Creating compressed stabilized
earth blocks (CSEBs) differs from rammed earth in that
the latter uses a larger formwork into which earth is
poured and manually tamped down. Rammed earth
methods result in forms that are larger than adobe or
individual building blocks (such as a whole wall, or
more, at any one time) and uncompressed.
CSEB is a block unit formed from a loose damp
mixture of laterite, cement and water, which is then
compacted mechanically to form a hydrated block that
is characterized by higher compressed strength and
improved durability as compared to a laterite block
produced in similar manner without the addition of
cement [3]. Typically, around 21MPa is applied in
compression, and the original soil volume is reduced by
about half [4].
Unlike burnt clay brick, CSEB and other earth products
are not burnt but are stabilized by pressure so their
carbon foot print and embodied energy is very low as
compared to conventional building materials. The
embodied energy and carbon emission of an average
kiln fired brick of size 22cm*10cm*7cm travelled 150
km is 2247.28MJ/m3 and 202.255 kgCO2 /m3
respectively whereas for an CSEB with 5% cement of
size 24cm*24cm*9cm has an energy of 572.58MJ/m3
and carbon emission of 51.531 kgCO2/m3 which is
almost one-fourth of the kiln brick [5]
Structural characteristics of CSEB
Both the mechanical and structural characteristics of
CSEB have been researched extensively - including
manufacturing technique, block density, level of
compaction, type and amount of stabilizer used, soil-
stabilizer ratio, addition of fibers or other additives,
curing conditions, temperature in the early days after
casting, etc. [6].
Raw Materials for production of CSEB
The primary raw material for the production of SCEB is
raw earth or soil. OPC cement in little quantities and
water, coarse sand or stone dust may be added
depending on soil quality. The physical properties of
soil have greater relevance in the manufacture of
compressed earth block. They include colour, particle
size break-up, structural stability, adhesion, bulk
density capillary, porosity, specific heat, moisture
content, permeability, linear contraction and dry
strength. Soil classified, as clayey sands are excellent
for making blocks. The optimum soil composition for
compressed soil/mud block is 7% gravel, 53% sand,
20% silt and 20% clay [7].
The Nigerian Building and Road Research Institute
(NBRRI)
The Nigerian Building & Road Research Institute
(NBRRI) was established by the Federal Government
of Nigeria to conduct integrated applied research and
development in the building construction sectors of the
economy. NBRRI is geared towards evolving
technologies and process to increase local content and
capacity utilization of alternative/local building
materials and evolving cost-effective methods of
providing shelter.
II. The NBRRI Interlocking CSEB
The NBRRI interlocking CSEB is made of suitable soil
(laterite) stabilized by cement of not less than 5% by
weight with a minimum compaction effort of 20MPa.
The NBRRI cement stabilized laterite block is based on
the concept of Compressed Stabilized Earth Block
(CSEB) and is produced by compressing a soil and
cement mixture with suitable moisture content in the
NBRRI Interlocking Semi-Automated Block Making
Machine. The machine has the basic advantage of
impacting adequate compressive effort on blocks to
achieve suitable and adequate compressive strength.
International Journal of Recent Engineering Science (IJRES), Volume 7 Issue 2 March - April 2020
ISSN: 2349 – 7157 www.ijresonline.com 15
The NBRRI interlocking CSEB is a technology that
employs dry stacking of blocks with nor mortar needed
for bonding of blocks during use in construction rather,
blocks interlock via tongue and groove joints at the
lateral and posterior positions [8].
Production process of the NBBRI Interlocking
CSEB The materials used for the production of the NBRRI
interlocking CSEB are basically laterite, cement and
water.
Laterite
The basic raw material for the production of the NBRRI
interlocking CSEB is laterite soil with good grain size
distribution and good cohesive performance. The soil to
be chosen should be free from organic matters.
Stabilizer (Cement)
The stabilizer used as binder to produce NBRRI
interlocking CSEB is 5% ordinary Portland cement.
This implies that the mix ration of laterite to cement is
19:1.
Water
Clean and portable water is used. Water that contains
salt and organic matters is avoided because it affects the
binding qualities of cement. Generally sea and stagnant
water are characterized by salt and organic matter
respectively.
There are five (5) processes in the production of
NBRRI CSEB interlocking, these includes the
following; [8].
i. Sieving of Soil
Usually when soil is brought from the field, it may
contain boulder and lumps. To obtain a powdery
material that can be efficiently mixed with
stabilizer (cement) the soil has to be sieved. This is
done manually or by passing the soil through a
locally constructed sieve (8ft by 4ft) of mesh 8-
12m.
ii. Mixing materials
Calibrated containers such as graduated buckets,
head pans, wheel barrow are used to measure the
exact quantity of required materials (i.e. laterite
and cement). This is achieved by volume or
weight. Mixing is done manually or in NBRRI
laterite mixer machine.
iii. Ejection of Blocks from the Machine
When ejecting the blocks from the machine, the
following points are taking into consideration:
If cracks appear, the moisture content of the mix is
checked and remix properly
If soil stocks to the mould, the moisture content and
mix are check, then the mould is cleaned
If the edges are rough, the moisture content of the mix
are checked, remixed and the mould cleaned
iv.
v. Stacking
The lower layers of the blocks in the stack are checked
for cracking. If cracks appear it can be due to many
reasons:
The ground is rough, which can be corrected by
leveling it with a layer of wet soil.
The stacking is too high and should be reduced, a
stacking of up to 5 layers is recommended.
vi.
Curing
The stacked blocks are covered with polythene. If water
drops are not seen on the internal surface of the
polythene, the polythene may have not been properly
fixed and therefore allows water to evaporate. The
blocks are cured for 21days.
Fig 1: NBRRI Interlocking CSEB
International Journal of Recent Engineering Science (IJRES), Volume 7 Issue 2 March - April 2020
ISSN: 2349 – 7157 www.ijresonline.com 16
Fig2: NBRRI Interlocking CSEB Making Machine
III. THERMAL CONDUCTIVITY OF NBRRI
INTERLOCKING CSEB
Block samples were moulded at different diameter and
thickness using the NBRRI Semi- Automated
Interlocking CSEB Machine and compressed at 20MPa.
The moulded block samples were exposed to controlled
fire at varying temperatures inside a kiln for duration of
1½ hours.
Table 1: Sample Dimensions
Dimension (mm) Diameter (D) Thickness (d)
Reading 1 110.80 16.04
Reading 2 112.84 16.80
Reading 3 111.63 16.99
Reading 4 111.53 17.17
Reading 5 111.15 16.85
Reading 6 112.50 16.12
Average 111.74 16.66
Table 2: Steady Temperatures Measured Using
Temperature (0C) 1 2
Before Interchanging 92.2 64.0
After Interchanging 92.0 64.2
Mean Temperature 92.1 64.1
Table 3: Cooling Rate of Block Sample after Heating
Temperature 73.4 72.2 71.2 69.5 68.7 67.8 67.1
(0C)
Time (S) 30 60 90 120 150 180 210
Temperature 66.4 65.4 65.2 64.5 64.0 63.4 62.9
(0C)
Time (S) 270 300 330 360 390 420 450
Temperature 62.3 61.7 61.2 60.4 59.8 59.3 58.5
(0C)
Time (S) 480 510 540 570 600 630 600
Figure 3: Plot of Temperature
t=
70 – 59
580 – 100 =
11
480
k = 7
22x 4 x
11
480 x
0.01488 x 380 x 0.9956
(0.11092)2x 28
k= 0.4765Wm-1K-1
Unit thermal conductance, U, is the thermal
conductance for a unit area of material and can be
determined by dividing the thermal conductivity of a
material by its thickness, as demonstrated in Equation
(1) [9].
U = 𝒌
∆𝒙 (1)
The heat transfer rate in each component of a building
system is then given by,
𝑞 = 𝑈𝐴∆𝑡 (2)
Where,
𝒒 = heat transfer rate (W)
𝑼 = unit thermal conductance (W/m2·K)
15.0
25.0
35.0
45.0
55.0
65.0
75.0
85.0
0 500 1000 1500 2000 2500 3000 3500 4000
Cooling Curve of NBRRI CSEB (Sample 2)
Time (S)
Expon. (Time (S))
T
t
International Journal of Recent Engineering Science (IJRES), Volume 7 Issue 2 March - April 2020
ISSN: 2349 – 7157 www.ijresonline.com 17
𝑨 = surface area normal to flow (m2)
∆𝒕 = overall temperature difference (K)
Table 4: Dimension of the NBRI CSEB
Dimension NBRRI CSEB
Length, L (cm) 23
Width, W (cm) 18
Area, A (cm) 414
∆𝒕 = 92.1 − 64.1 = 28 𝑘
𝑈 = 0.4765
𝑂.18= 2.647W/m2
q = 1.92 × 0.0414 ×28 = 3.068W
Table 5: Heat Transfer of NBRRI CSEB
NBRRI CSEB
Thermal conductivity 0.4765
(W/mK)
Thickness (m) 0.1800
Conductance (W/m2K) 2.6470
Area (m2) 0.0414
Heat Transfer (W) 3.0680
Table 2: Steady Temperatures Measured Using Two
Thermometers
Building Material Thermal
conductivity
(W/mk)
Specific
Heat
Capacity
(W)
Clay 3.252 19.12
Plywood 0.12 12158
Particle board
Hardwood
Cement mortar
Cement block
CSEB
0.0170
0.16
0.72
0.72
0.4765
1300
1255
780
835
3.06
This result shows that CSEB is the most energy
efficient walling material among the alternative walling
materials.
Advantages of Interlocking CSEBs
Energy saving. Earthen walls have a different thermal
behaviour than any other materials. As clay is just
stabilized and not burnt, it can still absorb and release
some moisture through evaporation and condensation.
Thus if the outside temperature is higher: the wall will
evaporate moisture. This will cool down the wall and
thus the building inside. And if the temperature is lower
outside: the wall will condense moisture. This will
create heat in the wall and thus the building inside. This
phenomenon is called “latent heat”.
Saves Cost. The main manufacturing cost of the block
involves only the cost of conveying the earth to the site,
a routine procedure since earth is a material within easy
reach of most building sites. Furthermore, if the earth
comes from the excavation work on the site itself, two
birds are killed with one stone, compounding the
savings. Technically, moreover, it is a very
advantageous material with great energy-saving
potential in heating and cooling terms.
Clean technology. No contamination or noise, gaseous
or thermal pollution of any type is produced during the
block manufacturing process.
Non-toxicity. The material gives off no type of
radiation or toxic product during its useful life. It has
low energy emission. It is observed that the energy
efficiency of CSEB having way less embodied energy.
Durability. It is a long-lasting and easily maintained
material; properly clad, it suffers no attacks from
micro-organisms.
Main Uses of CSEB
CSEB finds application in the following area:
As a normal load bearing masonry
As infill masonry
Special applications such as ventilations. Cable
duct, chamfers, vaults and arches etc
As reinforced masonry
RESULTS AND CONCLUSION
The thermal conductivity of the NBRRI CSEB in this
research is 0.4765 W/mk. This value was compared to
the thermal conductivity of other building/walling
materials. By comparison, CSEB can exhibit a third of
the thermal conductivity of say clay brick.
This research has proven that the NBBRI CSEB has
less embodied energy and global warming potential
than other conventional walling materials. Thus, CSEB
has the capacity for adaption as walling material as
compared to other walling materials due to it improved
energy efficiency and thermal capabilities.
The potential impact of choosing the NBRRI CSEB
over other walling materials in a building envelope in
terms of differing thermal conductivity was
International Journal of Recent Engineering Science (IJRES), Volume 7 Issue 2 March - April 2020
ISSN: 2349 – 7157 www.ijresonline.com 18
investigated. Based on thermal conductivity, The
NBRRI CSEB results in greatly reduced energy
consumption, global warming potential and economic
cost, saving up to 95% heating and cooling cost.
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[3] Adam, E. A., Compressed Stabilized Earth Block
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[4] Gideon T., Housing and Jobs for a Better Future. (World
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[5] Auroville Earth Institute (http://www.earth- auroville.co).
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Thermo Physical Characteristics of Economical Building
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[8] Danjuma, T. Eco-friendly Benefit of NBRRI CSEB, Int’l
Journal of Advanced Engineering and Science, 2018, Vol.
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